High performance non-zinc, zero phosphorus engine oils for internal combustion engines

ABSTRACT

A substantially zinc and phosphorous free lubricating oil meeting engine performance requirements contain an additive system containing metal detergents, at least one borated ashless dispersant, at least an amine antioxidant and a trinuclear molybdenum compound. The lubricant contains a minimum of 120 ppm boron and a minimum of 80 ppm molybdenum.

This application claims the benefit of U.S. Ser. No. 60/497,234 filedAug. 22, 2003.

FIELD OF INVENTION

The present invention is concerned broadly with lubricating compositionsand more specifically with lubricating compositions for internalcombustion engines that are substantially free of phosphorous and zinc.

BACKGROUND OF INVENTION

Contemporary engine oil technology uses zinc dithiophosphates (ZDTP) ormore specifically zinc dialkyldithiophosphate (ZDDP) for corrosion,oxidation and wear protection and metallic detergents for enginecleanliness. These additives are rich in sulfur, phosphorous and ashcontent, and play a critical role in meeting severe engine performancerequirements. Unfortunately phosphorous tends to deactivate thecatalysts typically employed for control of hydrocarbon emissions fromthe engine. Volatile sulfur is harmful to the catalysts used to controlNO_(x) emissions; and, zinc contributes to plugging engine exhaustparticulate filters. Although sulfur emissions can be reduced byformulating lubricant compositions using low sulfur base oils as much astwo thirds of the sulfur and almost all of the phosphorous present inengine oils is due to the use of ZDTP or ZDDP. Thus, there is a need forlow sulfur containing engine oils that are substantially free of zincand phosphorous and yet which do not adversely effect engineperformance. Indeed there is a further need for low sulfur,non-phosphorous, non-zinc engine oils that are particularly suitable foruse with low sulfur (<350 ppm) fuels. The present invention provides forthese and other needs.

SUMMARY OF INVENTION

In one aspect, the present invention is directed toward a lubricatingcomposition having low levels of sulfur, preferably below about 2000 ppmsulfur, and substantially no zinc or phosphorous, the compositioncomprising:

-   -   (a) a major amount of a base oil of lubricating viscosity; and    -   (b) an additive system comprising        -   (i) a metal detergent or mixture of metal detergents;        -   (ii) an ashless dispersant or mixture of dispersants, at            least one of which is a borated ashless dispersant;        -   (iii) an ashless aminic antioxidant or mixture of            antioxidants containing at least an aminic antioxidant; and        -   (iv) an oil soluble, phosphorous free, trinuclear molybdenum            compound.    -   (c) with the proviso that the composition has a minimum of 120        ppm boron and a minimum of 80 ppm molybdenum.

Another aspect of the present invention is directed toward a low sulfurcontaining lubricant composition which is substantially zinc andphosphorous free that is particular suitable for use in enginescombusting low sulfur fuels, the composition comprising a major amountof a low sulfur base oil, preferably below about 300 ppm sulfur and anadditive system comprising a combination of a metal detergent or mixtureof metal detergents, at least a borated ashless dispersant, an ashlessantioxidant or mixture of antioxidants containing at least an aminicantioxidant, and an oil soluble, phosphorous free, trinuclear molybdenumcompound, the composition having a B:Mo:N ratio in the range of about3:5:7 to about 5:1:18.

The lubricants of the invention are especially useful with fuelscontaining below about 350 ppm sulfur.

These and other aspects of the invention will become apparent from thedetailed description which follows.

DETAILED DESCRIPTION OF INVENTION

The lubricating compositions of the present invention will comprise amajor amount of a base oil of lubricating viscosity and a minor buteffective amount of a specific combination of dispersants, antioxidants,detergents and antiwear agents which do not contain zinc andphosphorous. Thus the compositions do not include zinc and phosphorouscontaining additives and as such are substantially free of zinc andphosphorous.

The base oils of the present invention will have less than about 300 ppmsulfur. Thus suitable base oils include highly refined Groups II and IIIbase oils as well as Groups IV and V oils and mixtures thereof.Preferred are Groups III, IV and V base oils.

The additive system of the invention includes a metal detergent ormixture of metal detergents, such as alkaline metal detergents. Usefulalkaline metal detergents are selected from calcium and magnesiumsulfonates, phenates and salicylates and mixtures thereof.

The amount of metal detergent will constitute about 1.5 to about 6.0 wt% based on the total weight of the composition. Preferably the detergentwill be a mixture of alkaline metal sulfonates, and phenates andsalicylates in the weight ratio of about 25:75:0 to 0:20:80.

The additive system includes a borated ashless dispersant or a mixtureof a borated ashless dispersant and non-borated ashless dispersants. Ingeneral, sufficient borated dispersants will be used to provide thecomposition with a minimum of 120 ppm boron. Useful borated dispersantsinclude sulfur and phosphorous free borated succinimides and succinicacid esters. Preferred borated dispersants are derivatives ofpolyisobutylene substituted with succinic anhydride and reacted withpolyethylene amines, polyoxyethylene amines and polyolamines(PIBSA/PAM). Useful non-borated ashless dispersants include sulfur andphosphorous free succinimides, carboxylic acid amides, hydrocarbylpolyamines and the like. Preferred non-borated dispersants are based on600 molecular weight PIB to 2800 molecular weight PIB as exemplified byLubrizol 6461, Lubrizol 6418, Hitec 646, Oloa 13000, ADX 222 and thelike.

In the practice of the invention it is preferred to use a mixture ofborated and non-borated ashless dispersants in the weight ratio of 1:9to 9:1. In any event, the total amount of ashless dispersant used in thecomposition is in the range of about 2.0 wt % to about 12.0 wt % basedon the total weight of the composition.

The additive system of the invention includes an ashless aminicantioxidant or mixture of antioxidants containing at least an aminicantioxidant. Useful aminic antioxidants include alkylated diphenylamine, alkylated phenylenediamine, alkylated phenyl alpha-naphthylamineand alkylated quinoline.

In addition to the aminic antioxidant supplementary antioxidants may beemployed. These include hindered phenols, hindered bisphenols,sulfurized phenols, sulfurized olefins, dithiocarbamates, phenothiazinesand the like.

Typically antioxidants used in the present invention will be a mixtureof non-borated phenolic and amine antioxidants. The weight ratio ofphenol to amine is in the range of 1.0:9.0 to 9.0:1.0. The preferredantioxidant is a mixture of hindered phenols and alkylateddiphenylamines. It also is preferred that the antioxidant be present inan amount ranging from about 0.25 wt % to 2.5 wt %, based on the totalweight of the composition.

The composition of the invention includes an oil soluble, phosphorousfree trinuclear molybdenum compound. Such compounds may be representedby the formula Mo₃S_(k)L_(n)Q_(z) where the L are independently selectedligands having organo groups with a sufficient number of carbon atoms torender the compound soluble or dispersible in the oil, n is from 1 to 4,k varies from 4 through 7, Q is selected from the group of neutralelectron donating compounds such as water, amines, alcohols, and ethers,and z ranges from 0 to 5 and includes non-stoichiometric values. Atleast 21 total carbon atoms should be present among all the ligands'organo groups, such as at least 25, at least 30, or at least 35 carbonatoms. The preferred ligands are dialkyl dithiocarbamates. In general,sufficient trinuclear molybdenum compound is used to provide thecomposition with a minimum of 80 ppm molybdenum. Thus, trinuclearcompound typical is present in about 0.05 wt % to about 1.50 wt %, basedon the total weight of the composition.

Importantly, the compositions of the invention are formulated to have aB:Mo:N ratio in the range of about 3:5:7 to about 5:1:18.

The compositions of the invention optionally may include other additivestypically used in formulating engine oils such as antifoamants, sealswell agents, viscosity index improvers and the like.

The invention will be further illustrated by the following examples.

EXAMPLE 1

A series of engine lubricants were formulated having the compositionsset forth in Table 1. Oil 1 included for comparative purposes had asulfur content of 3080 ppm and a phosphorous content of 960 ppm. Oils 2and 3 were substantially zinc and phosphorous free and had sulfur levelsof 1161 and 1483 ppm respectively. TABLE 1 Oil 1 Oil 2 Oil 3 SyntheticsSynthetics Synthetics Component Viscosity Grade Formulation Chemistry0W-40 0W-30 5W-30 Mixed Ashless Borated & non- 8 8 8 Dispersants boratedPIB succinimide/ester Mixed Ca/Mg sulfonate/ 3.35 4.3 4.3 Detergentsphenate/salicylate ZDDP Zinc 1.0 0 0 dithiophosphates Mixed Phenolic &1.0 1.5 1.5 Antioxidants Aminic antioxidants Mixed Friction Moly Trimer& 0.46 0.35 0.35 Modifiers ashless friction modifiers Mixed Silicone &non- 3.02 2.0 2.0 Defoamants/seal silicone swell agent/VI improvers BaseOil Group IV/V Bal. Bal. Bal. Ash (D874) Wt % 0.96 0.99 1.05 Zn Ppm 1000<5 <5 Mo Ppm 0 180 170 B Ppm 180 540 545 N Ppm (calculated) 1049 14941494 P Ppm 960 <5 <5 S (D2622-1) Ppm 3080 1161 1483

These oils were then subjected to the engine performance tests listed inTable 2. The results of these tests are also provided in that table.TABLE 2 Oil 1 Oil 2 Oil 3 Engine Oil Type Synthetics SyntheticsSynthetics Viscosity Grades PAO, PAO, Group III, 0W-40 0W-30 5W-30Special Remark Test Test Normal Low S, Low S, Method Measurement S/P/AshZn/P free Zn/P free HFRR¹ Ave. Friction 0.125 0.12 0.123 0.7 Kg/60 Hz/ %Ave. Film 0 96.5 81.4 0.5 mm/ Scar X/Y (mm) 0.3/0.7 .3/0.7 0.267/0.66760 min./75° C. Calc. Scar Area 0.165 0.165 0.14 Set One (mm2) HFRR¹ Ave.Friction 0.096 0.089 0.096 0.5 Kg/60 Hz/ % Ave. Film 4.66 90.8 95.7 1.0mm/ Scar X/Y (mm)  0.3/1.28 0.3/1.23 0.28/1.2  60 min./100° C. Calc.Scar Area 0.302 0.291 0.267 Set Two (mm2) Four-Ball Wear WSD (mm) 0.470.40 0.38 40 Kg/1800 rpm/ K Factor 30 min./200° F. (×10E−8) PDSC²Ramping @ Onset Temp 236 258.1 251.7 10° C. C/min. (° C.) Isothermal @Time (min.) 10.8 16.9 16.6 220° C. Hot Tube Test 1 = clean, 3 1 1 16hr./288° C. 9 = dirty Sequence IVA Cam Nose 56.9 6.7 wear (Micron) TotalWear 305 43.8 (Micron)¹HFRR = High Frequency Reciprocating Rig²PDSC = Pressure Differential Scanning Calorine Tray

The High Frequency Reciprocating Rig (HFRR) test results indicate thatoils 2 and 3 can lower the average friction by 1-4% in condition set oneand 0-7% in condition set two. Similarly, oils 2 and 3 can also increasefilm formation via electric contact potential (ECP) measurements from81-96% (versus 0% of oil 1) in condition set one and 91-96% (vs. 5% ofoil 1) in condition set two. Furthermore, the calculated scar area (fromthe multiply of X-axis) of oil 1 is larger than the scar area of oils 2and 3 (0-18% larger in condition set one and 4-13% larger in conditionset two). Clearly, these results indicate the low sulfur,phosphorus/zinc free oils protect the metal surface from wear by formingstronger films, lowering frictional force and significantly reducingwear better than normal S/P oil 1. These results are correlated withFour-ball wear results very well. As the data indicated, a reduction ofwear scar diameter (WSD) from 0.467 mm (oil 1) to 0.403 mm (oil 2) is14% and a reduction from 0.467 mm (oil 1) to 0.383 mm (oil 3) is 18%.

As illustrated in Table 2, very good antioxidancy is achieved with thelow sulfur, zinc/phosphorus free oils of the invention. As shown inPressure Differential Scanning Calorimetry (PDSC), the onset temperatureof oil 2 and oil 3 is 16-22 degrees higher than the result of oil 1(ramping method). Since oxidation rates generally double with about 10°C. increase in temperature, these results can be translated into about220% to 340% better in terms of control of viscosity or acid numberincreases or any other comparable measurements for control of oxidation.With the isothermal PDSC method, the oxidation resistance time is about6 minutes longer (55% better) than the result of oil 1.

Sequence IVA testing is a very critical engine test that is used toassess anti-wear performance of engine oils. As demonstrated in oil 2, alow sulfur, phosphorus/zinc free oil, passes Sequence IVA engine test(cam wear and piston cleanliness) while oil 1 with normalsulfur/phosphorus/ash levels, fails. Reduction in cam nose wear can beas great as 88% reduction when compared oil 2 to oil 1 (6.7 vs. 56.9)and the reduction in total wear is equally outstanding (86% reductionfrom 305 micron to 44 micron).

EXAMPLE 2

A series of zinc and phosphorus free engine lubricants were formulatedhaving the compositions set forth in Table 3. Oil 1 had a boron contentof 93 ppm and molybdenum content of 190 ppm whereas oils 2 had a boroncontent of 540 ppm and molybdenum content of 180 ppm. Oil 3 was free ofmolybdenum, but had a similar boron content to oil 2 (550 ppm). Theseoils were then subjected to the same engine performance tests (SequenceIVA) set forth in Example 1 and the results of these tests are providedin Table 3.

The Sequence IVA test results indicated that oil 2 meets wearrequirements (<120 micron) while oil 1 could not. Oil 3 also failed theengine test as molybdenum friction modifiers were removed from theformulation. Clearly, the boron-molybdenum synergism is needed in orderto achieve a satisfactory engine performance. Either the high boronalone or a combination of low boron and high molybdenum is notsufficient to meet the engine requirements. TABLE 3 Oil 1 Oil 2 Oil 3Synthetics Synthetics Synthetics Component Viscosity Grade FormulationChemistry 0W-30 0W-30 0W-30 Mixed Ashless Borated & non- 8 8 8Dispersants borated PIB succinimide/ ester and/or functionalized olefincopolymers Mixed Ca/Mg sulfonate/ 4.3 4.3 4.3 Detergentsphenate/salicylate Mixed Phenolic & 1.5 1.5 1.5 Antioxidants Aminicantioxidants Mixed Friction Moly Trimer 0.35 0.35 0.35 Modifiers &ashless Defoamants/seal Silicone & 2.0 2.0 2.0 swell agent/VInon-silicone improvers ZDDP Zinc 0 0 0 dithiophosphates Base OilPAO/Group V Bal. Bal. Bal. Ash (D874) Wt % 0.99 0.99 Zn Ppm <5 <5 <5 MoPpm 190 180 <0.5 B Ppm 93 540 550 N Ppm (Calculated) 878 1494 1453 P Ppm<5 <5 <5 Sequence IVA 289 44 134 7-Point Total Wear (Micron)

1. A lubricating oil composition having less than about 2000 ppm sulfurand substantially free of zinc and phosphorus comprising: (a) a majoramount of a base oil of lubricating viscosity; and (b) an effectiveamount of an additive system comprising: (i) a metal detergent ormixture of metal detergents; (ii) an ashless dispersant or mixture ofdispersants, at least one of which is a borated ashless dispersant;(iii) an ashless aminic antioxidant or mixture of antioxidantscontaining at least an aminic antioxidant; and (iv) an oil soluble,phosphorous free, trinuclear molybdenum compound. (c) with the provisothat the composition have a minimum of 120 ppm boron and a minimum of 80ppm molybdenum.
 2. The composition of claim 1 wherein the compositionhas a B:Mo:N ratio in the range of about 3:5:7 to about 5:1:18.
 3. Thecomposition of claim 2 wherein the additive system includes a mixture ofalkaline metal detergents selected from the group consisting of calciumand magnesium sulfonates, phenates, salicylates and mixtures thereof inthe amount of about 1.5 to about 6.0 wt % based on the total weight ofthe composition.
 4. The composition of claim 3 including a mixture ofborated and non-borated dispersants in the weight ratio of 1:9 to 9:1and wherein the total amount of ashless dispersant is in the range ofabout 2.0 wt % to about 12.0 wt % based on the total weight of thecomposition.
 5. The composition of claim 4 includes a mixture ofphenolic and amine antioxidants in the weight ratio of about 1.0:9.0 toabout 9.0:1.6 and wherein the total amount is in the range of about 0.25wt % to about 2.5 wt % based on the total weight of the composition andwherein the trinuclear molybdenum compound is present in an amount offrom about 0.05 wt % to about 1.50 wt %, based on the total weight ofthe composition.
 6. In the lubrication of an engine combusting a fuelcontaining below about 350 ppm sulfur, the improvement wherein theengine is lubricated with a composition comprising: (a) a major amountof a base oil of lubricating viscosity; and (b) an effective amount ofan additive system comprising, (i) a metal detergent or mixture of metaldetergents; (ii) an ashless dispersant or mixture of dispersants, atleast one of which is a borated ashless dispersant; (iii) an ashlessaminic antioxidant or mixture of antioxidants containing at least anaminic antioxidant; and (iv) an oil soluble, phosphorous free,trinuclear molybdenum compound. (c) with the proviso that thecomposition have a minimum of 120 ppm boron and a minimum of 80 ppmmolybdenum.
 7. The improvement of claim 6 wherein the composition has aB:Mo:N ratio in the range of about 3:5:7 to about 5:1:18.
 8. Theimprovement of claim 7 wherein the additive system includes a mixture ofalkaline metal detergents selected from the group consisting of calciumand magnesium sulfonates, phenates, salicylates and mixtures thereof inthe amount of about 1.5 to about 6.0 wt % based on the total weight ofthe composition.
 9. The improvement of claim 8 wherein including amixture of borated and non-borated dispersants in the weight ratio of1:9 to 9:1 and wherein the total amount of ashless dispersant is in therange of about 2.0 wt % to about 12.0 wt % based on the total weight ofthe composition.
 10. The improvement of claim 9 wherein includes amixture of phenolic and amine antioxidants in the weight ratio of about1.0:9.0 to about 9.0:1.6 and wherein the total amount is in the range ofabout 0.25 wt % to about 2.5 wt % based on the total weight of thecomposition and wherein the trinuclear molybdenum compound is present inan amount of from about 0.05 wt % to about 1.50 wt %, based on the totalweight of the composition.